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RESEARCH GROUP
QUANTITATIVE MRI IN MEDICINE AND BIOLOGY
Basic MRI principles
Yves De Deene
RESEARCH GROUP QUANTITATIVE MRI IN MEDICINE AND BIOLOGY
NMR
Nuclear Magnetic Resonance
MRS
Magnetic
Resonance
Spectroscopy
Molecular
Composition
Basic MRI principles
MRI
Magnetic
Resonance
Imaging
Spatial Tissue
Differentiation
MRR
Magnetic
Resonance
Relaxometry
Molecular
Dynamics
 Yves De Deene
RESEARCH GROUP QUANTITATIVE MRI IN MEDICINE AND BIOLOGY
MRS
MRI
MRR
Magnetic
Resonance
Spectroscopy
Magnetic
Resonance
Imaging
Magnetic
Resonance
Relaxometry
Spectra
Images
Relaxation times,
Diffusion coefficients
Basic MRI principles
 Yves De Deene
RESEARCH GROUP QUANTITATIVE MRI IN MEDICINE AND BIOLOGY
NMR imaging is non-invasive
Strong static magnetic field
Radiofrequent electromagnetic waves
Space and time dependent magnetic fields
Basic MRI principles
 Yves De Deene
RESEARCH GROUP QUANTITATIVE MRI IN MEDICINE AND BIOLOGY
Properties of the atomic nucleus
mp = 0,00000000000000000000000167 g
mp = 1,67.10-24 g
Water
+++
++
+
+ +++
qp = 0,00000000000000000016 C
qp = 1,6.10-19 C
H2O
Basic MRI principles
 Yves De Deene
RESEARCH GROUP QUANTITATIVE MRI IN MEDICINE AND BIOLOGY
Discovery of nuclear magnetic resonance
1938
Off
resonance
N
N
N
In resonance
Z
Isidor Isaac Rabi
Z
Molecular beam apparatus
H
z
H
z
Z
Spin reservoir
oven
Basic MRI principles
 Yves De Deene
RESEARCH GROUP QUANTITATIVE MRI IN MEDICINE AND BIOLOGY
Nuclear magnetic resonance in a block of parafin
1946
N
Block of parafin
IDC
B
Electromagnetic wave
with fixed frequency f
S
Edward Purcell
E
Absorption
-1/2
+1/2
IDC ~ B
B
2  f
B

Nobel price physics (Bloch & Purcell) in 1952
Basic MRI principles
 Yves De Deene
RESEARCH GROUP QUANTITATIVE MRI IN MEDICINE AND BIOLOGY
1946
Nuclear magnetic resonance mathematical description
The Bloch equations
L
G
B
Felix Bloch
Basic MRI principles
 Yves De Deene
RESEARCH GROUP QUANTITATIVE MRI IN MEDICINE AND BIOLOGY
Precession in a magnetic field
B
Basic MRI principles
 Yves De Deene
RESEARCH GROUP QUANTITATIVE MRI IN MEDICINE AND BIOLOGY
MRI signal generation
B0
B0
B0
COIL
Cryogenic magnet
EXCITATION PULSE
Gradient coils
Radiofrequency
transmit/receive coil
Water molecule
Basic MRI principles
Hydrogen proton transmits a
radiofrequent electromagnetic
wave (yellow) after excitation
by an RF pulse (red)
Image
Processing
(2D-FFT)
 Yves De Deene
RESEARCH GROUP QUANTITATIVE MRI IN MEDICINE AND BIOLOGY
MRI signal excitation / reception
Signal reception
Excitation
COIL
Basic MRI principles
OBJECT:
Spin system
COIL
OBJECT:
Spin system
 Yves De Deene
RESEARCH GROUP QUANTITATIVE MRI IN MEDICINE AND BIOLOGY
The first MRI scanner
1972
2.f = . B
Resonance condition
fulfilled
Raymond V. Damadien
Raymond V. Damadien
Inhomogeneous
magnetic field
First MRI scan
Basic MRI principles
 Yves De Deene
RESEARCH GROUP QUANTITATIVE MRI IN MEDICINE AND BIOLOGY
Current MR scanners
Clinical MR scanner
Open MR unit
Basic MRI principles
Animal MR scanner
Interventional MR unit
Mobile MR unit
 Yves De Deene
RESEARCH GROUP QUANTITATIVE MRI IN MEDICINE AND BIOLOGY
MRI signal generation
Yes, but... what about spatial encoding ??
?
10
9
10
6
10
3
10-3
1
10-6
10-9
MRI
10-9
10-12
10-6
10-3
10 6
SHF
UHF
VHF
HF
MF
LF
VLF
SLF
ELF
ULF
10 3
micro- Tera- IR
wave hertz
10 9
1012
10 3
1
visible
radiofrequency
1
Wave length
 (m)
10 6
Photon energy
E (eV)
X-ray CT
EHF
10-15
10-12
UV
1015
X-rays
1018
Gamma
-rays
1021
Frequency
f (Hz)
Interaction
with matter
Basic MRI principles
 Yves De Deene
RESEARCH GROUP QUANTITATIVE MRI IN MEDICINE AND BIOLOGY
MRI encoding
An analogon in acoustics
1
2
3
Basic MRI principles
 Yves De Deene
RESEARCH GROUP QUANTITATIVE MRI IN MEDICINE AND BIOLOGY
MRI encoding: slice selection
An analogon in acoustics
1
2
3
Basic MRI principles
 Yves De Deene
RESEARCH GROUP QUANTITATIVE MRI IN MEDICINE AND BIOLOGY
MRI encoding: Slice selection
X-gradient
B
z
Y-gradient
GRADIENT COILS
y-coil
1.52 T
z-coil
x-coil
Z-gradient
f = 64.8 MHz
64.8 MHz
Basic MRI principles
patient
 Yves De Deene
RESEARCH GROUP QUANTITATIVE MRI IN MEDICINE AND BIOLOGY
MRI frequency encoding
An analogon in acoustics
1
2
3
Frequency encoding
Basic MRI principles
 Yves De Deene
RESEARCH GROUP QUANTITATIVE MRI IN MEDICINE AND BIOLOGY
MRI frequency encoding
RF COIL
B
B
B
Fourier
transform
Basic MRI principles
 Yves De Deene
RESEARCH GROUP QUANTITATIVE MRI IN MEDICINE AND BIOLOGY
2D spatial encoding
Richard Ernst
Basic MRI principles
 Yves De Deene
RESEARCH GROUP QUANTITATIVE MRI IN MEDICINE AND BIOLOGY
Dephasing – T2* decay
In free space
In human tissue
IN PHASE
OUT OF PHASE
Basic MRI principles
 Yves De Deene
RESEARCH GROUP QUANTITATIVE MRI IN MEDICINE AND BIOLOGY
The spin-echo sequence
1949
EXCITATION
PULSE
(90°)
REFOCUSSING
PULSE
(180°)
TE/2
TE/2
N
Z
Basic MRI principles
 Yves De Deene
RESEARCH GROUP QUANTITATIVE MRI IN MEDICINE AND BIOLOGY
The spin-echo sequence
Slice selection
(90°)
SLICE SELECTION
B
z
1.52 T
f = 64.8 MHz
1.52 T
Basic MRI principles
 Yves De Deene
RESEARCH GROUP QUANTITATIVE MRI IN MEDICINE AND BIOLOGY
The spin-echo sequence
Phase encoding
(90°)
PHASE ENCODING
y
B
Basic MRI principles
 Yves De Deene
RESEARCH GROUP QUANTITATIVE MRI IN MEDICINE AND BIOLOGY
The spin-echo sequence
Frequency encoding
(180°)
(90°)
FREQUENCY ENCODING
B
y
1.43
Basic MRI principles
1.5
1.53 T
 Yves De Deene
RESEARCH GROUP QUANTITATIVE MRI IN MEDICINE AND BIOLOGY
The spin-echo sequence
180°
PULS
90°
PULSE
TE/2
180°
PULSE
90°
PULSE
TE/2
TE/2
TE/2
GSL
GRO
GPH
Basic MRI principles
 Yves De Deene
RESEARCH GROUP QUANTITATIVE MRI IN MEDICINE AND BIOLOGY
The spin-echo sequence
slice I
fc
180°
PULSE
90°
PULSE
fc
TE/2
180°
PULSE
90°
PULSE
TE/2
TE/2
TE/2
GSL
slice II
fc+Df
180°
PULSE
90°
PULSE
TE/2
TE/2
GSL
Basic MRI principles
 Yves De Deene
RESEARCH GROUP QUANTITATIVE MRI IN MEDICINE AND BIOLOGY
The spin-echo sequence
SLICE SELECTION
FREQUENCY AND PHASE ENCODING
2D-FOURIER
TRANSFORM
z
Mxy (x, y , z, t )  M0   (x, y , z, t )  e j ( x ,y ,z,t )
AMPLITUDE
IMAGE
Mxy (x, y , z, t )  Mx (x, y , z, t )  j  My ( x, y , z, t )
(f , f)
PHASE
(f)
M(t )   Mxy ( x, y, z, t )  dx dy dz
V
FREQUENCY
(f)
Basic MRI principles
 Yves De Deene
RESEARCH GROUP QUANTITATIVE MRI IN MEDICINE AND BIOLOGY
K-space
Mxy  M0   (x, y , z, t )  e j ( x ,y ,z,t )
t
t
t
0
0
0
with ( x, y, z, t )   B0t  x    Gx (t ')  dt '  y    Gy (t ')  dt '  z    Gz (t ')  dt '
For 3D imaging (ignoring relaxation)
S(k x , ky , kz )  M0   ( x, y, z)  e


 j  kx ( t )x  ky ( t )y  kz ( t ).z
V
For 2D imaging (z = z0)
S(kx , ky )  M0  ( x, y, z  z0 )  e

 j  kx ( t )x ky ( t )y

j k
 ( x, y, z  z0 )  C  S(k x , k y )  e 


dx  dy  dz
dx  dy
x ( t ) x  k y ( t )y

dk x  dk y
(x,y,z=z0)
S(kx,ky)
2D FFT
Basic MRI principles
 Yves De Deene
RESEARCH GROUP QUANTITATIVE MRI IN MEDICINE AND BIOLOGY
K-space
kx    Gx  t
Phase Encoding
Gradient
Spin-echo
ky    Gy  t
Mxy  M0   (x, y , z, t )  e
j ( x , y ,z,t )
Basic MRI principles
t
t
t
0
0
0
with ( x, y, z, t )   B0t  x    Gx (t ')  dt '  y    Gy (t ')  dt '  z    Gz (t ')  dt '
 Yves De Deene
RESEARCH GROUP QUANTITATIVE MRI IN MEDICINE AND BIOLOGY
K-space
k-space
Image space
IMAGINARY
REAL
IMAGINARY
REAL
FFT
MAGNITUDE
S(k x , ky )  M0   ( x, y, z  z0 )  e
MAGNITUDE
PHASE

 j  k x ( t )x ky ( t )y

Basic MRI principles

dx  dy
PHASE
j k
 ( x, y, z  z0 )  C  S(k x , k y )  e 

x ( t ) x  k y ( t )y

dk x  dk y
 Yves De Deene
RESEARCH GROUP QUANTITATIVE MRI IN MEDICINE AND BIOLOGY
Walking through K-space
The spin echo sequence
180°
PULS
90°
PULSE
TE/2
TE/2
ky
E
GSL = Gz
D
A
kx
B
C
GRO = Gx
GP
= Gy
H
A
B C D
Basic MRI principles
E
 Yves De Deene
RESEARCH GROUP QUANTITATIVE MRI IN MEDICINE AND BIOLOGY
Walking through K-space
The spin echo sequence
180°
PULS
90°
PULSE
TE/2
TE/2
ky
E
GSL = Gz
D
A
kx
B
C
GRO = Gx
GP
= Gy
Imaging time = TR. NEX.Nphase
H
A
B C D
Basic MRI principles
E
 Yves De Deene
RESEARCH GROUP QUANTITATIVE MRI IN MEDICINE AND BIOLOGY
Spin-lattice and spin-spin decay
Dipolar interaction
Spin-lattice decay T1
Spin-spin decay T2
Longitudinal relaxation
Transverse relaxation
B0
B0
time
Basic MRI principles
time
 Yves De Deene
RESEARCH GROUP QUANTITATIVE MRI IN MEDICINE AND BIOLOGY
Spin-spin decay and molecular dynamics
Hydrogen bridges
M
FREE
WATER
High mobility
t
M
INTERMEDIATE
LAYER
+
-
+
+
- O C - +
+
+
O
C
+
C
-

+
+ +
t
M
-
+
N
+
BOUND
LAYER
Low mobility
t
Protein, polymer, cell membrane
Basic MRI principles
 Yves De Deene
Anatomical imaging:
RESEARCH GROUP QUANTITATIVE MRI IN MEDICINE AND BIOLOGY
Multiple sclerosis
Anatomical imaging: Multiple sclerosis
Proton density
(transverse)
Proton density
(sagital)
Basic MRI principles
T2 weighted
(transverse)
T1 weighted
With contrastagent
Cluster analysis (T1w, T2w, PDw)
 Yves De Deene
Anatomical Imaging:
RESEARCH GROUP QUANTITATIVE MRI IN MEDICINE AND BIOLOGY
Arterio venous diseases
Arterio venous diseases
Arterio venous malformation (AVM)
T2 weighted
(transverse)
MR angiography
Thrombosis
T2 weighted
MR angiography
Basic MRI principles
Aneurism
MR angiography
MR angiography
Infarct (‘stroke’)
Proton
density
Proton
density
Neck trauma
T2 weighted
 Yves De Deene
Anatomical imaging:
OncologyRESEARCH GROUP QUANTITATIVE MRI IN MEDICINE AND BIOLOGY
Oncology
T2 weighted
(cyst)
T1 weighted with contrastagent
(Breast carcinoma)
Protondensity
(Brain metastasis)
T2 weighted
(chondrosarcoma)
T2 weighted
(cervix carcinoma)
Basic MRI principles
T2 weighted
(prostate tumor)
 Yves De Deene
Anatomical imaging
RESEARCH GROUP QUANTITATIVE MRI IN MEDICINE AND BIOLOGY
Bone and soft tissue
Bone and soft tissue
rheumatoid arthritis rheumatoid arthritis
knee
whrist
T2 weighted
(torn ligaments)
T2 weighted
(hernia)
Osteoporosis (femur)
Basic MRI principles
 Yves De Deene
I visited Copenhagen frequently after the war. At one point, I
gave a talk in Copenhagen, and then afterwards we met with
Bjerrum. Bjerrum was a chemist and a great friend of Niels
Bohr… Bohr said to him: “You know, what these people do is
really very clever. They put little spies into the molecules and
send radio signals to them, and they have to radio back what
they are seeing.” I thought that was a very nice way of
formulating it. That was exactly how they were used. It was not
anymore the protons as such. But from the way they reacted,
you wanted to know in what kind of environment they are, just
like spies that you send out. That was a nice formulation.
- Felix Bloch -